The invention relates to a light scanning head for needles in knitting machines, more particularly in circular knitting machines, an associated light scanning system and a method for testing needles in knitting machines with the light scanning system.
As a result of the very high loading to which needles are subjected in knitting machines such as, for example, single, fine rib, Jacquard and interlock circular knitting machines, needles of this type often break. In order to prevent the production of large quantities of waste, it should be possible to switch off a circular knitting machine as quickly as possible in the event of breakage of a needle hook or a needle foot.
It is therefore the object of the invention to provide a testing system which can be easily handled and recognizes a broken needle reliably and in good time.
To this end, according to a first aspect, the invention proposes a light scanning head for needles in knitting machines, with a first light wave conductor, which has a first end for supplying light radiation and a second end for transmitting the light onto a needle, and a second light wave conductor, which has a first end, which lies so close to the second end of the first light wave conductor that radiation reflected by the needle enters the second light wave conductor, and which has a second end, from which the reflected radiation emerges in order to be supplied to an evaluating unit.
According to an embodiment of the invention, the second end of the first light wave conductor and the first end of the second light wave conductor are guided as close as possible up to the needle. In this case, the light wave conductors are preferably formed by optical fibers, particularly preferably by two monofil conductors, whose cross sections, which are preferably circular, contact one another.
In both embodiments, the light wave conductors can be formed by optical fibers, it being possible to arrange the optical fibers of the second light wave conductor between the optical fibers of the first light wave conductor, so that together they form a combined light wave conductor, of which part of the fibers are used for transmitting the light radiation and another part for returning light reflected by the needle.
According to another aspect of the invention, a light scanning system for needles in knitting machines is proposed, with a control unit, which comprises at least a light source and an evaluating unit with a receiver, at least a first and a second light wave conductor, the first light wave conductor having a first end, which is connected to the light source in order to supply light to the first light wave conductor, and a second end, which is arranged for transmitting the light onto a needle, and the second light wave conductor having a first end, which is secured so close to the second end of the light wave conductor that radiation reflected by the needle enters the second light wave conductor, and having a second end, which is connected to the evaluating unit, so that the reflected radiation is supplied to the receiver.
Furthermore, a method for testing needles in knitting machines with a light scanning system is proposed, in which firstly light wave conductors are arranged in such a manner that the needles reflect light transmitted by a first light wave conductor and light reflected by the needles enters the second light wave conductor, then with intact, correctly arranged needles a basic signal sequence of the signals detected by the receiver over one or more runs of the knitting machine or one or more revolutions of the circular knitting machine is recorded and/or a basic signal sequence determined for the given machine is deposited in a store of the control unit, and then prior to or during operation of the machine a signal sequence of the signals detected by the receiver over one or more runs or revolutions of the machine is recorded, which is compared with the basic signal sequence, a fault being reported if the signal sequence cannot be brought into sufficient correspondence with the basic signal sequence.
The measured signals are preferably digitized by means of a threshold criterion, so that the digitized signals represent the frequency of the passage of the needles. In order to detect possible needle breaks, it is then preferable to proceed as follows: From the known running velocity of the knitting machine (that is, for example, the rotational speed in the case of circular knitting machines) and the positionsxe2x80x94which are also known for a given machinexe2x80x94of the holders for the needles, which are fitted to a greater or lesser degree with needles according to the knitting pattern, the frequency is determined, at which the individual reflected light signals of the needles which are actually present can occur using the measurement according to the invention. Since the holders for the needles are spaced equidistantly in the machine, reflection signals can only occur at intervals corresponding to the spacing of the needle holders of the machine, i.e. the reflection signals can only occur at frequencies corresponding to an integral multiple of the distance between adjacent needle holders. It is therefore possible to provide a sequence of very short time windows for the evaluating electronics, whose spacing corresponds to the time required by adjacent needles in order to enter the light beam. A given value can then be set for each time window, so that as a result of the given measurement tolerances it is ensured in practice that the reflected light of each needle is measured. In this manner, fault signals which are caused by disturbances between the individual needles, e.g. nap or the like, can be eliminated.
The invention also teaches a particularly preferred method of evaluating the signal sequences recorded during the monitoring of the knitting machine, which are compared with the basic signal sequence as explained above. As defined above, the signal sequence is the measurement result relating to the light reflected by the needles during operation (or optionally during a pause in operation), i.e. the monitoring signal. The basic signal sequence corresponds to the ideal xe2x80x9cnominalxe2x80x9d state of the needles (i.e. the state with intact needles which are correctly fitted). The comparison of the signal sequence with the basic signal sequence is time-consuming. This means that a certain time span occurs between the measurement of the signal sequence and the receiving of the result relating to the comparison of the signal sequence with the basic signal sequence. This time span should be as short as possible, so that the machine can be switched off as quickly as possible in the event of a fault. If the machine continues to run for too long once a fault has occurred, not only is material unnecessarily lost, but serious damage to the machine can also occur, e.g. as a result of the broken needle. Consequently, it is provided according to a preferred development of the method of the invention that basic signal sequence types corresponding to possible arrangement patterns of the needles are defined and are stored in a computer, a basic signal sequence recorded with intact, correctly arranged needles is associated with one of the basic signal sequence types, and the comparison of the recorded signal sequences with the basic signal sequence is effected as a function of the associated basic signal sequence type.
It is provided in a further preferred embodiment of the method according to the invention that time windows (xc2x1xcex94t) are provided, which can be adjusted during the recording of the basic signal sequence and/or the signal sequence for the occurrence in time of the signals of the reflected light. This development of the invention offers the advantage that the measurement accuracy when determining the signal sequence can be adjusted as a function of the desired quality requirements by the user of the method which is carried out using a correspondingly programmed computer. If the time window is set to be relatively short (narrow), then the needles must be at their provided location with relatively little tolerance. Otherwise a fault would be detected. In contrast, if a relatively long time window is provided, this means that the measurement is relatively tolerant in respect of bending of the needles. For the quotient of the said time window and the time span which lapses between the passage of two directly adjacent needles (with minimum spacing) at the light scanning head, a value of 20%, for example, is provided. This value is adjustable during the monitoring of the machine, depending on the quality requirements.